The main goal of the Calan-Yale Deep Extragalactic Research (CYDER) Survey
X-ray survey is to study serendipitous X-ray sources detected by Chandra in
an intermediate flux range (10-15 to 10-12 ergs/s) that comprises most of
the X-ray background. A total of 267 X-ray sources spread over five archived
fields were detected. The log N - log S distribution obtained for this sample
is consistent with the results of other surveys. Deep V and I images were
taken of these fields in order to calculate X-ray-to-optical flux ratios.
Identifications and redshifts were obtained for 106 sources using optical
spectroscopy from 8 m class telescopes to reach the optically faintest
sources, to the same level as deeper X-ray fields like the Chandra Deep
Fields, showing that the nature of sources detected depends mostly on the
optical limit for spectroscopy.

Name
The name of the X-ray source using the 'CXOCY' prefix followed by the
J2000 equatorial coordinates of the X-ray source, as registered with the CDS
Dictionary of Nomenclature of Celestial Objects, e.g.,'CXOCY JHHMMSS.s+DDMMSS'.

RA
The Right Ascension of the X-ray source in the selected equinox.
This was given in J2000.0 coordinates to a precision of 0.01 seconds of time
in the original table.

Dec
The Declination of the X-ray source in the selected equinox.
This was given in J2000.0 coordinates to a precision of 0.1 arcseconds
in the original table.

Offset
The offset between the X-ray source and the closest optical
counterpart, in arcseconds. Only counterparts with positional offsets
of smaller than 2.5 arcseconds are listed here (and were used in the
analysis reported in the reference paper).

Hardness_Ratio
The hardness ratio (HR) is defined as HR=(H-S)/(H-R), where
H and S are the counts in the hard (2.0 - 8.0 keV) and soft (0.5 - 2.0 keV)
X-ray bands, respectively

Vmag_Limit
This parameter is set to '>' if there was no optical
counterpart in the V band within 2.5" of the X-ray source, and the quoted
V magnitude is a 5-sigma upper limit.

Vmag
The CTIO V-band magnitude of the closest optical counterpart to
the X-ray source that lies within 2.5". Objects in the V-band and I-band images
were matched by position, allowing a maximum offset between objects of 1".

Imag_Limit
This parameter is set to '>' if there was no optical
counterpart in the I band within 2.5" of the X-ray source, and the quoted
I magnitude is a 5-sigma upper limit.

Imag
The CTIO I-band magnitude of the closest optical counterpart to
the X-ray source that lies within 2.5". Objects in the V-band and I-band images
were matched by position, allowing a maximum offset between objects of 1".

SB_Flux
The soft-band (0.5 - 2 keV) flux of the X-ray source, in erg/s/cm2.
For sources with 60 or more counts, the X-ray spectra were fit using a
power-law model with the appropriate Galactic column density for that
direction, while for weaker sources, fits using the same model but for
a fixed power law slope of 1.7 were used.

HB_Flux
The hard-band (2 - 8 keV) flux of the X-ray source, in erg/s/cm2.
For sources with 60 or more counts, the X-ray spectra were fit using a
power-law model with the appropriate Galactic column density for that
direction, while for weaker sources, fits using the same model but for
a fixed power law slope of 1.7 were used.

Redshift
The redshift of the optical counterpart to the X-ray source
(only available for sources with spectroscopic identification).

SB_Lx
The soft-band (0.5 - 2 keV) luminosity of the X-ray source, in erg/s,
in the observed frame, without accounting for k-corrections or for absorption.
Hence, the simple formula, Luminosity = (4 pi x D2 x flux), was used.

HB_Lx
The hard-band (2 - 8 keV) luminosity of the X-ray source, in erg/s,
in the observed frame, without accounting for k-corrections or for absorption.
Hence, the simple formula, Luminosity = (4 pi x D2 x flux), was used.